Introdution

On 11jun03 (4am AST) we scanned 3C454.3 using
the vlba recorder and the cband receiver. The radar interface was run at
10 hz sampling of a 5 mhz band while the interim correlator was run with
a 25 Mhz band at 10 hz sampling. Two other vlba antennas were also used.
After 3C454.3 set the calibrator J2334+0736 was tracked for awhile.
The vlba correlator sampled at .13 seconds. There
were 7 patterns. Pattern number 4 has arecibo tracking the source the entire
time (since we passed through low za for this pattern).

The routine used the pattern corstarotf . The driving
routine was in src.11jun03. Each pattern consisted of

39 strips through the source followed by 3 circles around the source center.

Each strip was 25 arcminutes (great circle) long (+/-12.5 aminutes).

The next strip started 180./39. degrees clockwise from the end of the previous
strip.

Each strip took 18 secs with 5 secs to move to the start of the next strip.
(18+5)*39= 15 minutes for the strips.

The circles started after the strips. They were at radii: 9.45,10.15,10.85
arcminutes and had a drive rate of 1.5 arcminute/sec. Before each circle
the telescope went on source for 3 seconds. Each circle took about 90 seconds.

The pointing trajectory preprocessor was turned off for this experiment
(pnt pre 0). The telescope was commanded to the positions once a second.
It waited to be on position at the start of each pattern and at the on
source start of each circle. It did not wait to be at the start of each
strip. It just tried to do as well as it could.

The pointing program had its fast dump mode enabled. It output the time(millisecs),
az, greg,ch positions in 1/10000 of a degree at about 25 hz. The data was
4 byte bigendian integers.

The first plots shows the az,za
offsets from 3C454.3 for the 6 patterns. The axis are great circle
offsets in az,za from the center of the source. Each plot has the positions
for the start of the pattern up to the positioning for the start of the
next pattern. The circles started at the right of each plot (3 hours on
a clock face).

Fig Top: za position vs utc hour. The start of each pattern is flagged
in red. The smooth line before each start was tracking on source. At the
end of the fifth pattern the horizontal line is where we stopped moving
to get off source and adjust the power levels.

Fig Middle. This is the time interval between samples of the az,za encoders.
The mean value was 40 millisecs.

Fig bottom: A blowup of the middle plot. At each 1 sec tick it took twice
as long to record the position since the computer was also busy collecting
other data.

The top plot is the amplitude versus time for the patterns (excluding the
circles). The red horizontal line is the clippping level used to define
what points were at the source peak.

The central plot is the phase at the peaks. Jumps of 2 pi radians have
been removed. The phase at the peaks wanders slowly by a few hundred
degrees. The red line is a high order polynomial fit to the phase.

The bottom plot shows the phase residuals after the fit has been removed.